1. Field of the Invention
This invention relates to a vibration control system for controlling transmission of vibrations from a vibration source, such as an engine, to a base supporting the vibration source.
2. Prior Art
Conventionally, a vibration control system of this kind has been proposed, e.g. by Japanese Provisional Patent Publications (Kokai) Nos.59-23139 and 59-65640, which comprises a vibration control assembly having an electrostrictive element arranged across a vibration-transmitting path, to which is applied voltage varying in synchronism with a repetition cycle of vibrations transmitted via the path to thereby absorb the vibrations by causing electrostrictive strain of the electrostrictive element.
According to this prior art, however, the electrostrictive element per se can be very easily affected or even broken by the strain. To overcome this inconvenience, the vibration control assembly is constructed such that a pair of plates are arranged on both sides of the electrostrictive element and the plates are fastened by means of a bolt to apply a compressive force (i.e. axial tension of the bolt) on the element. However, the vibration control assembly with this construction suffers from a problem that load is repeatedly applied to the bolt with oscillatory displacement of the electrostrictive element, so that the bolt may be loosened or broken by fatigue, which makes it difficult or even impossible for the vibration control assembly to support the vibration source. On the other hand, if the axial tension of the bolt is too weak, the electrostrictive element may undergo pealing-off and hence the assembly may be broken, which makes it impossible to support the vibration source, whereas if the axial tension of the bolt is too strong, the displacement of the element is limited by the axial tension of the bolt, which prevents positive and accurate control of transmission of vibrations from the vibration source to the base on which the vibration source is supported.